Foam components are commonly combined with wire or steel form innersprings in mattress, seating and other flexible support structures. Early versions included foam layers which were either attached directly to a wire innerspring or simply held in position by overlying upholstery. Smaller foam components are designed to fit within spaces of the innerspring. As described in the referenced related application, a new approach to the integration of innersprings and foam components involves welding or bonding of mating foam components to form a unibody structure which fits with an innerspring, forming a unitized steel and foam structure which provides flexible support.
Different types of foam and foam parts have been used extensively in seating and bedding as flexible support material. Semi-rigid open and closed cell foams of polyethylene, polyurethane or polystyrene have been used in combination with other components and load-bearing structures, such as wire form innersprings and framing to form flexible supports, such as described in U.S. Pat. Nos. 5,048,167; 5,469,590; 5,467,488 and 5,537,699 and 5,787,532. In most of these spring support products, the foam pieces surround or interfit with spring elements, and rely on mechanical connection with the spring elements to keep the foam pieces in place. Foam pieces have also been adhesively bonded and combined with innersprings. The types of foams used in these applications are typically open-cell polyurethane and latex materials, which can be effectively bonded by compatible adhesives. The open-cell structure of these types of foams results in easier compression or lower ILD which is suitable for many bedding and seating applications, particularly for support surface or topper layers underneath upholstery. They are not generally utilized as structural members in a mattress or support cushion in seating. Also, polyurethane and other non-thermoplastic type foams cannot be bonded or welded by any heat-source process due to their decomposition properties.
Some foam shapes have been used integrally with springs to augment or otherwise support metal spring structures, as shown for example in U.S. Pat. Nos. 5,133,116; 5,239,715; 5,467,488 and 5,687,439. Because this type of use of foam relies on the surrounding metal structure to hold it in place, the foam itself is not in the form of a unitized three-dimensional support structure with its own load-bearing capacity.
Another use of foam in connection with an innerspring is disclosed in U.S. Pat. No. 5,787,532, wherein an extruded foam piece is used as a perimeter wall to an innerspring, with fingers which mechanically engage the coils of the innerspring. While this provides vertical support at the perimeter of the innerspring, it relies on mechanical attachment to the innerspring for the correct orientation. It also only provides support primarily in the vertical direction and does nothing to stabilize the innerspring in the lateral or horizontal directions.
One type of foam which has been used for these types of applications is closed-cell polyethylene foam which is molded or extruded by known processes into desired shapes. Closed-cell foam has greater support properties due to the fact that each closed cell contains a gas which maintains the cells in an inflated state when under compression, as compared to open-cell foams from which a substantial volume of air is displaced when compressed.
Latex and polyethylene foam is commonly used in slab form as cushioning or dampening layers in mattresses and seating, held in place relative to an innerspring simply by surrounding upholstery. Alternatively, latex foam can be readily molded, and has been molded about innersprings to form a foam-encased mattress. This type of combination of foam and innerspring does not include any internal foam components which provide three-dimensional flexible, or which are bonded to any other components of a mattress or other flexible support device.